The present invention relates to an accumulator for use in a hydraulic control circuit for an automatic transmission of a motor vehicle, etc.
The automatic transmission uses a rotary hydraulic clutch for shifting of a speed ratio. In order to alleviate a sudden change in hydraulic pressure for the clutch, an accumulator is provided to a hydraulic passage to a clutch drum. If, during disengagement of the clutch, the clutch drum as released from an engagement state rotates at high speed, hydraulic pressure due to centrifugal force is produced within a hydraulic chamber in the clutch drum, discharging oil in the same way as a pump. At the same time, oil is sucked from a hydraulic control valve via the hydraulic passage. Referring to FIG. 3, in order to prevent the clutch from falling into a semiengagement state due to hydraulic pressure produced by centrifugal force operating on sucked oil, JP-A 68-308257 teaches to arrange to the accumulator 1 a check valve 4 for allowing an inflow of air into a working pressure chamber r.
With this prior art, since the accumulator 1 is disposed in a higher position than that of the hydraulic control valve, a change in the oil surface due to an increase in the oil volume on variations in temperature or due to an inclination of the motor vehicle fails to make the check valve 4 immersed in oil, which continues to function and carries out air suction in case of necessity.
With the prior art accumulator, however, the check valve 4 by way of a different part is built into a piston 2. Specifically, as shown in FIG. 3, a check valve unit is constructed so that a check ball 8 is disposed in a valve cylinder 5 having a through hole 6 across which a check pin 7 is arranged. As a result, an engagement portion of the piston 2 with the check valve 4 necessitates machining with a high accuracy, resulting in not only an increase in the number of processes of assembling work and a manufacturing cost, but a possible omission of parts such as the check pin 7, etc.
Moreover, considerable attention is required for securing sealing of the engagement portion which is a fundamental function. Additionally, a through hole 9 for receiving the check pin 7 should be formed in the valve cylinder 5, which becomes a fact or of aggravating problems of the number of processes of assembling work, a manufacturing cost, and a sealing.
It is, therefore, an object of the present invention to provide an accumulator for use in a hydraulic control circuit which enables a reduction in the number of processes of assembling work and a manufacturing cost, and an elimination of the problem of sealing.